1. Field of the Invention
The present invention relates to a switch device, and more particularly, to a structure for coupling a driving bar of a push button switch and a handling knob.
2. Description of the Prior Art
FIG. 5 is a cross sectional view showing an example of a conventional switch device. Push switch 1 is soldered to a printed circuit board 2 with terminals 3 projecting from the bottom. Contact means (not shown) are provided in the interior of case 4 which forms an outer shell of said push switch 1. A driving bar 5 having a coupling groove 5a projects from the top end of case 4. Driving bar 5 reciprocates vertically in the figure, and said contact means are switched when said driving bar 5 reciprocates. A frame 7 is mounted on said printed circuit board 2, and handling knob 6, molded of synthetic resin, slidably fits into frame 7 and moves up and down in FIG. 5. Said handling knob 6 is provided with a protrusion 6a and a pair of hooking pieces 6b,6b extending downward from the top inner surface of handling knob 6. The lower end of both hooking pieces 6b,6b are provided with nails 6c,6c. These hooking nails 6c,6c are coupled to said coupling groove 5a of driving bar 5, wherein the bottom surface of said protrusion 6a is in contact with the top surface of the driving bar 5. The length l is the distance from the inner ceiling of the handling knob to the bottom of the means which couple the handling knob to the driving bar.
The operation of the switch device constructed as aforementioned will be explained hereinafter.
In the off state of the push switch 1 shown in FIG. 5, the driving bar 5 and the handling knob 6 coupled to the driving bar 5 are raised by the resilient force of the returning spring contained within the case 4 (not shown). When the top of handling knob 6 is pushed down by a finger or the like, the handling knob 6 moves downward into the frame 7. This pushing force is transmitted to the driving bar 5 by the protrusion 6a and forces the driving bar 5 downward so that the push switch 1 is switched from off to on. The push switch 1 is locked in the on state by a lock mechanism (not shown) provided to the push switch 1. When the handling knob 6 is pushed again, the lock mechanism is released, and the driving bar 5 and the handling knob 6 are raised by said returning spring, so that the push switch 1 returns to the off state as shown in FIG. 5.
To couple the handling knob to the driving bar, the nails 6c must be snapped into the groove 5a. Before being snapped into the groove 5a, the nails 6c must first fit over the top of the driving bar 5 above the groove 5a. The hooking pieces 6b must be sufficiently flexible for the nails 6c to fit over the top of the driving bar. Ensuring this flexibility requires that the length of the hooking pieces 6b, which coincides with the length l in FIG. 5, be sufficiently long. Providing sufficiently long hooking pieces to guarantee this flexibility has been a significant factor hindering the miniaturization (i.e. making thin) of the switch device.